Parkinson's Researchers Focus On Pesticide Use

April 1, 2001|By LAURA BEIL The Dallas Morning News

Scientists wonder what the Rev. Billy Graham and Janet Reno have in common.

One answer: Parkinson's disease. The minister and the former attorney general are two of the more than 1 million Americans with the condition. But scientists can't say what common feature triggered the disease in those two and not another two. Or those million and not another million.

Parkinson's strikes when brain cells vital to muscle movement begin rapidly dying. For more than a decade, scientists have suspected that something in the environment might be a culprit.

The latest findings have strengthened that suspicion.

"I think we've got as good a chance now as we've ever had of finding a cause," said William Langston, president of the Parkinson's Institute, a nonprofit research organization in California.

Pesticides are the theory most under investigation, but scientists are also examining whether drinking well water, working with organic solvents, welding or even some aspect of country living might be to blame. These and other possibilities will be on the agenda when many of country's top Parkinson's experts share the findings this month at the Society of Toxicology's annual meeting in San Francisco.

Although the idea of an environmental accomplice for Parkinson's isn't new, two recent reports caught researchers' attention, said Dr. Kenneth Olden, director of the National Center of Environmental Health Sciences. The first appeared in the Journal of the American Medical Association in 1999. In it, Langston and his colleagues from the Parkinson's Institute described a study of almost 20,000 twin brothers who served in World War II. After examining the men who were diagnosed with Parkinson's, the researchers concluded that genetics had no major role in the disease when it appears after age 50. Only a small fraction of cases affects younger people.

"It was that study that convinced me that the environment is doing something here, and we need to find it," Olden said.

Then, in December, researchers from Emory University in Atlanta published a landmark paper linking pesticides to Parkinson's. For the first time, scientists were able to give rats a condition eerily similar to Parkinson's disease, right down to the brain cells, with the pesticide rotenone.

"I am very impressed with the pesticide data," said Olden, who is leading the Parkinson's discussion at the toxicology meeting.

Before there were pesticides, there was Parkinson's disease, however. Rotenone -- used to control bugs, and even fish populations in lakes -- is also similar to natural compounds that certain fungi and plants use to defend themselves.

Parkinson's investigators started focusing on pesticides in the 1980s, when a chemical called MPTP contaminated a synthetic form of heroin. When injected, MPTP left drug users with a disease almost identical to natural Parkinson's. MPTP turned out to be a chemical cousin of the pesticide paraquat.

Researchers then began examining farmers and others who are heavily exposed to pesticides. "Some studies reported an increase in Parkinson's as high as sevenfold," said Dr. Sadik Khuder of the Medical College of Ohio. Last year, in the journal Neurotoxicology, Khuder and his colleagues considered 19 studies on pesticide exposure and the risk of Parkinson's, looking for a trend. Some studies found a high risk, while a couple didn't show any relationship. Overall, though, pesticide exposure about doubled the risk of getting the disease, Khuder concluded.

In scientific terms, though, even twice the risk of Parkinson's isn't a huge number, and there still isn't enough evidence to indict pesticides, Khuder said.

The Parkinson's Institute may soon have that kind of data, Langston said. Researchers there are studying annual questionnaires that some pesticide applicators fill out to renew their licenses. The surveys would have started before any symptoms of disease.

Farming and fumigating might not be the only occupations that carry a higher risk for Parkinson's. Studies have also suggested that welders are more likely to get the disease. In January, researchers from Washington University School of Medicine in St. Louis reported that welders who have Parkinson's appeared to get the disease earlier than did other Parkinson's patients.

"If we can demonstrate that welding clearly brings on Parkinson's earlier than you would expect that would be the first evidence that something in the environment can actually bring on [Parkinson's] disease," said Dr. Brad Racette, whose study appeared in the journal Neurology.

If scientists can figure out how some substances make certain brain cells die, the findings might offer a way to prevent or treat Parkinson's, said Washington University's Racette.

"I think it's going to be the only way we're going to truly cure this disease," he said. "Until we figure out what causes it, we don't know what stops it."

Emory's Dr. Tim Greenamyre, who led the studies of rotenone, agreed. "We need to figure out exactly how rotenone is killing the cells, what the mechanisms are," he said. "With that knowledge in hand, we can begin to develop drugs that may block those steps."

But most people who get Parkinson's -- such as Billy Graham and Janet Reno -- aren't farmers or welders. Perhaps some people are just especially vulnerable to certain chemicals. In the end, scientists say, the cause of Parkinson's will probably be some combination of a person's heredity and environment.